Modelling the biodegradation kinetics of BTEX contaminated groundwater

Document Type : علمی - پژوهشی


1 Faculty of Earth Sciences, ShahidBeheshti University, Tehran, Iran

2 Faculty of Earth Sciences, ShahidBeheshti University, Tehran, Iran Research Institute of Applied Sciences (ACECR), ShahidBeheshti University, Tehran, Iran


Introduction: Petroleum hydrocarbons releases into the groundwater resources (both in saturated and unsaturated porous media) as a consequence of accidental spills during the transport, refining and storing stages especially in oil producing countries. There is no study related to cleaning of oil polluted groundwater in Iran due to the complexity of conditions governing groundwater aquifers. Benzene, toluene, ethylbenzene and xylene isomers (known as BTEX) are the most dangerous among other hydrocarbons due to their high solubility and carcinogenic potential.  This research is aimed at the bioremediation kinetics modelling of BTEX contaminated groundwater.Materials and methods: Bacteria isolation was performed by enrichment of polluted groundwater samples taken from the site of Tehran Oil Refinery. The Pseudomonas sp. BTEX-30 strain was selected among isolated bacteria for biodegradation kinetic modelling due to its high performance in BTEX biodegradation. Kinetic experiments were carried out in 500 ml glass vials with Teflon screw caps to prevent any BTEX vapour leakage. Upstream unpolluted groundwater was selected as the base solution and pH values of samples were adjusted to 7.6. Samples were incubated in a vertical rotary shaker with 100 rpm, 35 centigrade degrees for 72 hours. Kinetic experiments were performed for the single substrate with a concentration of 250 mgL-1 and the mixed substrate with a concentration of 500 mgL-1 BTEX (1:1:1:1). Different moisture contents were used to find the optimum moisture content for the biodegradation in the unsaturated zone.Results and discussion: Results show the Monod equation had the best fit for the experimental kinetic data. Maximum specific biodegradation rates in single substrate experiments were 0.45 h-1, 0.43 h-1 and 0.35 h-1 for benzene, toluene, and ethylbenzene, respectively. Pseudomonas sp. BTEX-30 strain was not able to degrade m-xylene in single substrate experiments and the maximum specific biodegradation rates in the mixed substrate experiments were 0.44 h-1, 0.45 h-1, 0.38 h-1 and 0.33 h-1 for benzene, toluene, ethylbenzene, and m-xylene, respectively.m-Xylene was degraded in mixed substrate experiments in the presence of benzene and toluene due to Increased cell growth and introduction of the enzymes incorporating in m-xylene degradation.Conclusion:Pseudomonas sp. BTEX-30 strain was able to degrade BTEX compounds in liquid and unsaturated soil with 20% soil moisture; however, the optimum soil moisture content for biodegradation was obtained at 60 %.


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